fix(tunnel): resolve UDP stream interruption and add KCP protocol support

- Increase UDP listener default TTL from 5s to 30s to prevent idle disconnect
- Add mux keepalive config (15s interval, 45s timeout) to tunnel relay handler
- Add KCP as tunnel chain transport protocol with keepalive and UDP mode default
- Add KCP protocol option to tunnel UI (frontend)
- Remove generic 'tcp' fallback key from KCP metadata to prevent false TCP mode
- Simplify forward service config by removing unused tunnelTLSProtocol parameter

go-gost/x/dialer/kcp/metadata.go

@@ -42,7 +42,7 @@ func (d *kcpDialer) parseMetadata(md mdata.Metadata) (err error) {
 	if d.md.config == nil {
 		d.md.config = kcp_util.DefaultConfig
 	}
-	d.md.config.TCP = mdutil.GetBool(md, "kcp.tcp", "tcp")
+	d.md.config.TCP = mdutil.GetBool(md, "kcp.tcp")
 	d.md.config.Key = mdutil.GetString(md, "kcp.key")
 	d.md.config.Crypt = mdutil.GetString(md, "kcp.crypt")
 	d.md.config.Mode = mdutil.GetString(md, "kcp.mode")

go-gost/x/internal/util/kcp/config.go

@@ -40,7 +40,7 @@ var (
 		SnmpLog:      "",
 		SnmpPeriod:   60,
 		Signal:       false,
-		TCP:          false,
+		TCP:          false, // default UDP mode (use tcpraw when true)
 	}
 )
 

go-gost/x/listener/kcp/metadata.go

@@ -45,7 +45,7 @@ func (l *kcpListener) parseMetadata(md mdata.Metadata) (err error) {
 	if l.md.config == nil {
 		l.md.config = kcp_util.DefaultConfig
 	}
-	l.md.config.TCP = mdutil.GetBool(md, "kcp.tcp", "tcp")
+	l.md.config.TCP = mdutil.GetBool(md, "kcp.tcp")
 	l.md.config.Key = mdutil.GetString(md, "kcp.key")
 	l.md.config.Crypt = mdutil.GetString(md, "kcp.crypt")
 	l.md.config.Mode = mdutil.GetString(md, "kcp.mode")

go-gost/x/listener/rudp/metadata.go

@@ -8,7 +8,7 @@ import (
 )
 
 const (
-	defaultTTL            = 5 * time.Second
+	defaultTTL            = 30 * time.Second
 	defaultReadBufferSize = 8192
 	defaultReadQueueSize  = 1024
 	defaultBacklog        = 128

go-gost/x/listener/udp/metadata.go

@@ -8,7 +8,7 @@ import (
 )
 
 const (
-	defaultTTL            = 5 * time.Second
+	defaultTTL            = 30 * time.Second
 	defaultReadBufferSize = 8192
 	defaultReadQueueSize  = 128
 	defaultBacklog        = 128